The present invention relates to a magneto-optical effect distance measuring device and a measuring rig incorporating this device, these being more particularly adapted to the monitoring of the closing of aircraft doors.
The closing of the doors in an aircraft is at present signalled to the flight deck by virtue of micro-contacts disposed in the surround of the doors.
This device is often criticized for providing unreliable information which generates false alarms, the latter usually being due to mechanical or electrical impairments of the micro-contacts themselves or caused by deformations of the hull of the aircraft, which produce a defect in the sealing of the door to its casing when the door is closed and reduce the pressure exerted on the contacts.
Moreover, the all-or-nothing binary operation of the micro-contacts does not make it possible to advise the flight deck and the aircraft""s internal pressurization system of the sealing of the doors, it being possible to determine this accurately only by measuring, along the entire perimeter of the doors, the distances which, in the closed position, separate the sills for supporting the doors on their casings.
To solve this problem it is possible to envisage the use of ultrasound sensors or optical sensors, but the use of these sensors requires wiring which increases the weight breakdown of aircraft. By way of indication, for a long-haul aircraft, the wiring up of 50 sensors requires not less than 4 kms of cabling, thereby increasing the weight breakdown by around 15 kgs if optical fibres are used, and by around 36 kgs and 52 kgs if coaxial cables or shielded pairs, respectively, are used.
The aim of the invention is to alleviate the aforesaid drawbacks.
Accordingly, the subject of the invention is a device for measuring the distance separating two members which can be displaced one with respect to the other by magneto-optical effect comprising a permanent magnet fixed on one of the members and an electro-optical device fixed on the other member, characterized in that the electro-optical device comprises:
a diode emitting an optical beam,
a Faraday-effect magneto-optical film disposed, on the one hand, between a polarizer and an analyser and, on the other hand, in the magnetic field of the magnet when the two members are in proximity to one another, the optical beam passing through the assembly,
and a photodiode receiving the optical beam retransmitted by the analyser so as to transform the luminous intensity of the beam into an electrical signal whose amplitude depends on the distance separating the two members when they are in proximity to one another.
The subject of the invention is also a rig for measuring distance between two members which can be displaced one with respect to the other, characterized in that it comprises a specified number N of sensors coupled by a single optical fibre to an emitting optical diode and a receiving photodiode, each sensor comprising a permanent magnet fixed on one of the members and an electro-optical device comprising:
a Faraday-effect magneto-optical film disposed, on the one hand, between a polarizer and an analyser and, on the other hand, in the magnetic field of the magnet when the two members are in proximity to one another,
and an optical fibre of specified length which is different for each sensor coupled by a first end to the input of the polarizer and the output of the analyser, and coupled by its second end, by way of an optical coupler, to a first end of the single optical fibre for coupling the N sensors to the photo-emitting diode and to the receiving photodiode (15), the second end of the single optical fibre being coupled to the emitting diode and to the receiving photodiode.
According to another possible mode of implementation of the invention, in order to embody a sensor, it will be possible to use a magneto-optical film disposed between the polarizer and a return mirror for returning the beam emitted by the emitting diode to the polarizer, the return mirror and the polarizer having the role of analyser.
The device according to the invention has the advantage of employing only static opto-electronic elements, thereby imparting high reliability to the systems incorporating this device.
It also has the advantage that it makes it possible to measure, with an accuracy of around 1%, small spacings between mechanical members a few millimetres apart, this possibly allowing, when applied to an aircraft, effective monitoring of the latter""s pressurization system as a function of the distances measured in the space located between the sill of the doors and their position of support on the opposite casings.
When applied to the construction of measuring rigs comprising several sensors, the invention has another advantage in that it makes it possible to use just a single optical fibre to remotely transmit the N items of information originating from the N sensors, this exhibiting an appreciable weight saving. Moreover, the use of an optical fibre as linking means also offers the possibility of transmitting other information on the same fibre, such as the temperature for example, or of integrating, without any particular adaptation, the measuring rig thus constructed into a fibre optic network.
The measuring rig according to the invention also has the advantage of being highly reliable since it makes it possible to detect any malfunctioning of an element of the rig which is manifested either through the appearance of a spurious signal, or through an abnormal amplitude of a signal.
Other characteristics and advantages of the invention will become apparent in the description which follows in conjunction with the appended drawings which represent:
FIG. 1 is a basic diagram of a distance measuring device according to the invention,
FIG. 2 is a first exemplary implementation of devices according to the invention making it possible to compensate for the variations in sensitivity of the various elements making up each device as a function of temperature.
FIG. 3 is a distance measuring rig implementing various devices according to the invention in conjunction with a remotely placed acquisition device.
FIG. 4 is an embodiment of a device according to the invention operating according to the basic principle of FIG. 1.